The present invention relates to an agricultural grinder-mixer, and more particularly, to a mixing tank configuration having an improved internal mixing assembly for augmenting the proper circulation of material contained in the tank.
Most present day grinder-mixers comprise a vertical mixing assembly mounted concentrically within a vertical mixing tank having a cylindrical upper portion and a conical downwardly converging lower portion. The mixing assembly comprises a centrally located mixing auger mounted for rotation on a vertical axis within a tubular housing. An inlet opening is provided in the housing at its lower end and a discharge opening is provided at the top of the housing. During a mixing operation, material is conveyed in a generally circuitous path. The auger continually transfers material from the bottom of the tank upwardly through the auger housing to the top of the tank whereupon it is discharged through the opening and allowed to gravitate back down toward the lower portion of the mixing tank. Commercially available apparatus of this type is illustrated by U.S. Pat. No. 3,780,993 issued Dec. 25, 1973, to Charles M. Kline, one of the joint inventors of the present invention.
The conical portion of the mixing tank configuration of the grinder-mixer described above functions to direct material inwardly towards the central mixing auger as it settles or gravitates downwardy during circulation. Since the horizontal cross section of the tank decreases as the walls converge inwardly, the material is compressed as it settles causing certain crop materials, especially under moist and/or extremely tough conditions, to form a cluster of relatively solid material. This is illustrative of a problem commonly encountered during operation of a tank having a conventional conical shaped lower portion. Material moving downwardly in the tank tends to build up in the area between the lower walls of the tank and the auger housing. This buildup, commonly referred to as "bridging," restricts free downward flow of material to the base of the mixing tank and thereby impedes the circuitous flow of material and diminishes effectiveness of the central mixing auger. Certain crop conditions lead to more bridging and many times shutdown is necessary to permit manual removal of material from plugged areas.
One prior art arrangement devised to overcome the problem of bridging in the lower tank is shown in U.S. Pat. No. 3,780,993 mentioned above. In this arrangement, the central mixing auger is provided with flighting having a lower section with relatively wider outside dimensions. This configuration is designed to increase the volume of material displaced per revolution and thereby effectively circulate material contained in the tank. Although this type of auger has been generally successful, its overall efficiency drops off under certain crop conditions due to shortcomings stemming from the conical configuration of the tank. This patent also features a plurality of outwardly projecting extensions on the lower auger flighting. As the mixing auger assembly is rotated, the extensions engage and agitate surrounding material to break up clusters of material in the vicinity of the auger and permit the material to gravitate more freely to the base of the tank. Consequently, the extensions further enhance overall circulation of feed material within the tank during a mixing operation. Although this feature generally improves the mixing capability under adverse conditions, it is not entirely satisfactory in that it tends to create turbulence during circulation of dry crop material peculiar to certain regions.
Another prior art approach that has been proffered as a solution to the problem of bridging in the lower tank portion of grinder-mixers is disclosed in U.S. Pat. No. 3,667,734, to A. D. Skromme et al, issued June 6, 1972. In this patent, the tank walls of the grinder-mixer are vertical and when material gravitates to the bottom of the mixing chamber during operation it is engaged by the blade of a long sweep arm rotating with and extending outwardly from the auger shaft. The arm sweeps across a path parallel to and encompassing the entire bottom of the tank. A similar sweep arm is employed in the vertical mixing tank disclosed in U.S. Pat. No. 1,576,018, issued Mar. 9, 1926, to R. B. Wolf. In this type of apparatus the tendency of material to wedge under the sweep arm could result in an upward force component causing obvious deleterious effects. This problem is partly alleviated if a guide is used to restrain the outer end. Another shortcoming inherent in a vertical sidewall type configuration stems from the need for a head of pressure for the sweep arm to operate effectively, without which the arm has a tendency to merely slide under the material without changing its relative position in the tank.
This disadvantage is even more prevalent at the end of an unloading operation, i.e., where the absence of a full load affects the ability of the sweep arm to radially urge material toward an unloading port. Thus, the sweep arm seems to operate best under full load conditions but conversely full load conditions tend to cause wedging.
There exists still another prior art approach to the problem of bridging in grinder-mixers having an inverted conical-shaped lower tank wall portion inclined inwardly for guiding material toward the central mixing auger assembly. For example, apparatus is sold by the Koehring Farm Division of Des Moines, Iowa, wherein the mixing assembly comprises an upper cylindrical auger and a lower auger portion having an inverse frusto-conical shaped core. In this arrangement, this inclined wall commences at the approximate center of the tank and the bottom of the tank is completely covered by the lower core section, as shown and described in Koehring brochure No. 15D472NWC. A similar configuration is disclosed in U.S. Pat. No. 3,589,684, issued on June 29, 1971, to Bernard Dixon. The Dixon patent also shows a mixing tank with a vertical mixing assembly having a frusto-conical shaped lower core section on a common shaft with an upper cylindrical auger. The upper and lower auger sections are journalled in the tank for rotation within a housing that is flared at the bottom in a shape adapted to accommodate the lower conical portion of the auger. As in Koehring, the lower core completely covers the tank bottom. Lastly with respect to Dixon, even though the flared enclosure section has slotted apertures, the conical portion of the housing under many crop conditions would tend to cause bridging between it and the tank wall due to the convergence of material with no means to rapidly take it away. Bridging problems are exceptionally acute under conditions where crop material is damp as is the case in many areas of the word where grinder-mixers are employed.